Critical Risks, Hazards, & Concerns

King tides in Richmond near 580

Bay Area communities face a range of natural hazards, including flooding, wildfires, earthquakes, landslides, and drought. Many of these hazards stem from the region’s mediterranean climate and location in an active fault zone. Scientists predict that climate change will exacerbate the effects of natural hazards, amplifying concerns for human health and safety, ecosystem resilience, and economic stability. Anticipated hazards include substantial near-term seismic events and higher risk of liquefaction for bay muds and artificial fill, longer and drier droughts during summer months, saltwater intrusion into aquifers, accelerated sea level rise and more powerful storm surges, warmer mean daily air and water temperatures, changing salinity and sediment trends, ocean acidification, decreases in water supply, and more frequent and intense wildfires. These hazards present challenges and uncertainties for biological communities and ecosystems in addition to human health and economic well-being.

Adaptations to these challenges will require flexible management approaches and an integrative perspective which considers the impacts of climate change on the Bay’s estuarine-river system from changing watershed and ocean factors. Resilient design approaches should safeguard water quality, native species, critical infrastructure and vulnerable communities while promoting energy efficiency, water conservation, health and wellbeing and multi-benefit outcomes. The following sections highlight some of the most relevant risks to guide design thinking for the Resilient By Design challenge, which include: (1) sea level rise and storm surge, (2) heat and drought; (3) water quality degradation; and (4) liquefaction. It is important to note that this is not an exhaustive list but rather a glimpse into the relevant areas of concern to inform resilient designs for the purpose of this design challenge.

Sea Level Rise and Storm Surge

Accelerated sea level rise and increased storm surge are projected to directly impact residents, habitats, businesses and infrastructure located in low-lying areas close to the Bay’s edge. According to a recent report (Griggs 2017), emissions of the last decade position us along the highest scenario considered by the last IPCC report, RCP 8.5. If current emission trends continue through this century, Bay sea levels will likely rise 0.6-1.1 feet by mid-century and 1.6-3.4 feet by 2100. There is a 1-in-20 chance that San Francisco will see a sea level rise of more than 4.4 feet by 2100 and a 1-in-200 chance that it will rise more than 6.9 feet (Table 1b, Griggs 2017). Sea level will continue rising beyond 2100.

Storm surge is also of great concern, as current projections show up to 3 feet of additional sea level rise in the San Francisco Bay during storm events. The region also receives about a foot of variation with El Nino/La Nina fluctuations in temperature between the ocean and atmosphere. The frequency of nuisance flooding will increase with sea level rise. For more details, explore NOAA’s Sea Level Rise Viewer and Our Coast Our Future’s Flood Map to visualize the projected impacts of different sea level rise and storm surge scenarios for specific areas within the Bay.

Sea level rise and storm surge also threaten to inundate critical infrastructure, which could have widespread implications across the Bay. For example, many wastewater treatment plants are located along the shoreline or at the edge of the baylands, leading to future uncertainties in sewage disposal, nutrient flows and water quality impacts. Highways are also of great concern as intermittent or permanent inundation could delay emergency vehicles, overcrowd other transit systems and interrupt economic activities. San Francisco, Oakland and San Jose International Airports are found in low-lying areas adjacent to the Bay, posing major economic concerns as these airports generate billions of dollars in annual business revenues and provide hundreds of thousands of jobs.

The Bay Area has a mediterranean climate which means dry, warm summers and wet winters with typical rainfall occurring between October and March. Accumulating scientific evidence indicates a shift to drier and warmer summers with more variable winter precipitation that may mean longer periods of drought and, when rains occur, more intense storm events.

Climate change presents altered regional patterns for temperature and precipitation which will pose uncertain impacts to endemic species within the Bay and surrounding rivers. Mean daily air temperatures are on the rise, causing higher evapotranspiration rates which create uncertainties for snowpack reserves and future water supply. Similarly, mean daily water temperatures are on the rise, causing long-term concerns for native species if temperatures surpass a specific threshold linked to high mortality rates. Examples of vulnerable endemic species include Delta smelt (Hypomesus transpacificus) and Chinook salmon (Oncorhynchus tshawytscha). Projected increases in estuarine salinity and decreases in suspended sediment concentrations will also have uncertain impacts on endemic species and habitats. Resilient designs should consider the needs of native species with respect to these challenges and explore ways to anticipate and adapt.

The water quality of freshwater aquifers close to the Bay’s edge as well as the Bay itself are at risk of degradation due to sea level rise and other stressors exacerbated by climate change. More instances of saltwater intrusion will likely occur in groundwater reserves near the Bay’s edge-- an occurrence that typically results from over-pumping. In some instances, sea level rise could pose pollution risks to the Bay by saturating subsurface contaminants suspected to persist from historical contamination sites (e.g., superfund site at Alameda Naval Air Station). In addition, leaching from landfills positioned around the Bay’s edge have potential to further decrease water quality (see liquefaction section for more details).

Seismicity is an imperative parameter to consider to ensure the future structural integrity of a

site’s design. There is a greater than 70% chance that at least one major earthquake of magnitude 6.7 or greater will strike somewhere in the Bay Area within the next 25 years. The risk posed by such a quake is amplified in areas built upon bay mud or artificial fill, which are susceptible to land liquefaction. Seismic precautions need to be taken where appropriate and land use on bay mud or bay fill need to be evaluated for increased risks due to the nature of the development. For example, the Bay has numerous inactive landfills around its margin, some of which have been built in liquefaction zones. Sea level rise and seismic activity could undermine the integrity of composite liners engineered to keep capped pollutants within landfills from entering the Bay or groundwater reserves. Excavation of landfill material would likely be very expensive and difficult to achieve without leaching toxic pollutants in the process, leading to increasing challenges to safeguard Bay water quality and human health.

Many of the concerns and hazards described above are interconnected and pose amplified risks when overlapping in geography. As mentioned previously, the categories of hazards described are intended to highlight the main concerns in the Bay Area relevant to this design challenge. Depending on the nature of the site analyzed, it may be necessary to analyze additional hazards outside of these categories before moving forward with a design idea or approach.